Train noise
Nature
Train noise is vehicle noise made by trains. Noises may be heard inside the train and outside.
Subway systems, light rail transit and freight trains can send loud train noise into neighborhoods. Organizations such as the World Health Organization and the U.S. Environmental Protection Agency have set guidelines for noise level decibel limits for rapid transit. Noise levels can be reduced by installing noise barriers next to the track. Traditional clickety-clack sounds occur as a result of gaps in the rail to allow for thermal expansion. On most railways, the gaps are opposite each other and if the carriages are about the same length as the rails, an even clickety clack sound is generated. In the USA the rail joints are staggered, so not being opposite each other, a different and irregular sound is heard.
Source: Wikipedia
Broader
Type
(E) Emanations of other problems